(1) Field of the Invention
This invention relates to a method for treating radioactive waste water, and more particularly, it relates to a method for allowing those corrosive radionuclides, other radionuclides and fission-products which are contained in the radioactive waste water to be adsorbed and captured by mordenite, thereby rendering these radioactive materials harmless to man.
(2) Description of the Prior Art
During operations of the light-water type reactor, heavy metals such as Fe, Ni, Mn, Cr, etc contained in the building materials of the reactor are attacked by corrosion and gradually dissolved in the cooling water. When the cooling water passes by the core, these metals are irradiated with neutrons and converted to corrosive radionuclides. Most of these nuclides stay in the primary cooling system and this causes such abnormalities in the reactor as local corrosion and stress corrosion. In addition, since the amount of such nuclides produced increase in proportion to the operation time of the reactor, they will have accumulated in great quantities at bends valves and pumps of the primary cycling system by the time that the operation of the reactor has been discontinued.
Another reason for the accumulation of radioactivity is the releasing of fission-products into the primary cooling system. In particular, if fuel cladding materials break due to corrosion and cracks, a large amount of the fission-products is released in the cooling water, and part of them may even leak out of the reactor.
Fission-products and corrosive radionuclides are also observed during the reprocessing of neutron irradiated nuclear fuels. No technology has to date been developed for insuring safe removal and recovery of these radioactive materials. There is therefore need that such technology be immediately developed, and this need is particularly great for the recovery of Cs-137 by reason of its high yield and long half-life (30 years). Furthermore, because Cs-137 is valuable as a source of heat, power, and gamma rays, efficient and economic recovery of this element can play a very important role in energy conservation.
In the conventional art, ion exchange resins have been employed to remove a variety of radioactive materials from the primary cooling water in the light water type reactor. Low and intermediate level radioactive nuclides produced in the course of reprocessing of neutron irradiated nuclear fuels have also been eliminated by means of using an organic ion exchange material. But such conventional method has many disadvantages in that the organic ion exchanger itself is susceptible to radiation damage and, also, a slight amount of light metals, heavy metals or fission-products cannot be captured by the exchanger. Other drawbacks are that not only is the ion exchanger poor in anti-radioactivity and heat resistance but also it eventually has to be discarded.
As explained above, there has long been a great need for improving the conventional method of separating, removing and recovering radioactive materials from radioactive waste water for ensuring easy, safe and efficient separation, removal and recovery of said radioactive materials.
The present inventors have accomplished this invention by noting the fact that zeolites, especially mordenite, have great acid resistance, heat resistance and anti-radio-activity as well as great ability to capture radioactive nuclides.